1. Field of the Invention
The present invention relates to a bag forming-filling-packaging machine which allows a pair of heat-seal bars disposed to oppose to each other across a tube film which moves in a longitudinal direction to carry out block motion in the same direction as that of the film, the bag forming-filling-packaging machine keeping constant to an utmost extent a moving procedure speed of the seal bars in the same direction as that of the film.
2. Description of the Prior Art
Generally, the bag forming-filling-packaging machine transfers a belt-shaped film while forming the same into a cylindrical shape, transfers an object to be packaged into the tube film at equal distances, and cross seals the tube film by a pair of seal bars to separate the packaged object from one another. When a belt-shaped film having a low melting degree is used in the bag forming-filling-packaging machine, it is necessary to elongate the heating time of the belt-shaped film as long as possible, therefore both the seal bars which grip the tube film with pressure are moved in the same direction as that of the belt-shaped film for a fixed time, and after the sealing is completed, both the seal bars must be brought out from an orbit of the belt-shaped film and returned to their original positions. In short, both the seal bars are allowed to carry out block motion.
Conventionally, JP7-291234 A discloses that a seal bar supporting frame is allowed to reciprocate along a transfer orbit of a tube film by revolution of a crankshaft, a pair of seal bars provided on the seal bar supporting frame are moved toward and away from each other, thereby allowing both the seal bars to carry out the block motion. However, only one half of the revolution orbit of the crankshaft can be used as an advancing region of the seal bar supporting frame. Further, a region where speed is extremely lowered exists in top and bottom dead centers of the revolution orbit sandwiching a stopped point. Therefore, there is a problem that the movement of the seal bars can be made constant only through about 120xc2x0.
It is an object of the present invention to move the tube film at a constant speed through one half region of a revolution orbit of a crankshaft, the seal bars closing the tube film between front and rear packaged objects, and evacuating the film from a cut formed in the closed portion.
The present invention provides a bag forming-filling-packaging machine comprising: a seal bar supporting frame which reciprocates along a transfer orbit of a tube film for packaging therein an object; a pair of seal bars disposed on the frame; and a crank mechanism which transmits a swinging motion of the arm having a support shaft on its one end as its fulcrum to the seal bar supporting frame through a connecting rod, thereby allowing the frame to reciprocate along the transfer orbit of the tube film, wherein both the seal bars are allowed to carry out block motion by a combination motion of the reciprocating motion of the frame, and approaching and separating motions of the pair of seal bars disposed on the frame such as to sandwich the tube frame, and while the tube film is being griped with pressure by the seal bars, air in the film is sucked and removed through a cut formed in a pressure-gripped region of the film, and then the cut is heated and sealed, characterized in that the bag forming-filling-packaging machine further comprises: a mechanism for slidably engage a slider supported by a crankshaft with a guide formed along the arm, and swings the arm by the crankshaft which is revolved by a servo motor; and a controller which defines opposite side regions of the arm swinging region as deceleration regions, and sends a calculation signal to the servo motor such that a swinging speed of the arm becomes constant in a region, in which a rotation angle of the crankshaft is 180xc2x0, inside the deceleration regions.
According to the present invention, due to the above structure, an open end of the arm which swings by a circular revolution motion of the crankshaft swings in an arc shape around the one end support shaft. Therefore, as the support shaft approaches the center of the revolution of the crankshaft, the arm moves the seal bar supporting frame forward in a one half region of the revolution circle of the crankshaft, i.e., in a region of a revolution angle of 180xc2x0 or greater, and moves the seal bar supporting frame backward at high speed in a region of remaining 180xc2x0 or less. In short, as a distance from the center point of the revolution circle to the one end support shaft center of the arm is shortened, the retreating region of the seal bar supporting frame is shortened, and it is possible to increase the forward region of the support frame correspondingly. If calculation data for keeping constant the swinging angle speed of the arm in the revolution angle region of 180xc2x0 is stored in the memory, whenever the crankshaft reaches the revolution angle region of 180xc2x0, the controller controls the rotation speed of the servo motor such that the swinging angle speed of the arm becomes constant. As a result, it is possible to carry out the relatively long time sealing operation which carries out the vacuum suction procedure in the tube film by both the seal bars and the heat sealing procedure through the cut in a stepwise manner without lowering the efficiency.